Spinal fixation system

ABSTRACT

A spinal implant system for correcting spinal deformities and abnormalities includes an elongated spinal rod configured to be implanted adjacent the spinal column and spanning across several vertebral levels. A number of fixation elements, such as spinal hooks, are provided for engaging vertebrae at a number of vertebral levels. At least some of the fixation elements includes an elongated stem projecting from a vertebra engaging portion. The stems of each of the fixation elements are connected to the spinal rod by way of a rod connector having a one-piece body defining a rod channel adapted to receive the spinal rod therethrough, a stem bore adapted to receive a stem therethrough, and a threaded bore. The stem bore and rod channel intersect to permit contact between the rod and the stem of a fixation element. The threaded bore intersects either the rod channel or the stem bore so that a set screw threaded into the threaded bore bears against the spinal rod or fixation element stem. As the set screw is tightened in the bore, the spinal rod and stem are clamped together to form a rigid construct. The rod channel includes a channel opening to permit top-loading of the rod connector. The fixation element stem may include external threads to receive a threaded fastener for temporarily threading onto the stem when the implant construct is at an initial posterior level above the spine. As the fastener is threaded onto the stem of each fixation element, the instrumentation is drawn down to a lower final level adjacent the vertebrae.

This application is a division of application No. 08/000,278, filed Jan.4, 1993, still pending.

BACKGROUND OF THE INVENTION

The present invention concerns a spinal fixation system, particularly asystem for posterior fixation of the spine for the treatment of spinaldeformities. Specifically, the system contemplates various componentsinterconnected together by way of elongated rods extending along thespinal column.

The treatment of spinal deformities and injuries has evolvedsignificantly since the 1970's. Spinal deformities, such as scoliosisand kyphosis, as well as fractures, spondylolisthesis, stenosis, tumorsand other medical indications have been treated using a system ofrelatively rigid rods spanning the vertebral column. One such system forcorrecting spinal deformities is the TSRH® system provided by DanekMedical, Inc. of Memphis, Tenn. One embodiment of the TSRH® system isshown in FIG. 1. In this TSRH® rod system, a pair of rods 11 and 12 spanthe length of the spinal column, particularly from the lower lumbarvertebrae to the thoracic vertebrae. A number of fixation hooks 13 areengaged to the rods by eyebolts 14 at various vertebral levels along theconstruction. These hooks are of well known construction and include aclaw for grabbing segments of a specific vertebra. The TSRH® system alsoprovides means for engaging the sacrum for a firm foundation for therigid construct. A transverse connector 15, provided by Danek as itsCross Link® connector, provides lateral engagement between the parallelrods. In known constructions, a number of transverse connectors 15 canbe situated at various locations along the rods as necessary to providean adequate and stable constinct.

The TSRH® spinal system, as well as other systems of this type, permitrigid and semi-rigid segmental instrumentation of the spine using aselection of hooks, and in some instances bone screws or bolts thatengage the pedicle of the vertebra.

In these previous hook and rod spinal systems, correction of spinaldeformities is achieved primarily through de-rotation of the rods. Hooksattached to the rods exert forces at key points of the deformed spine tocorrect the particular deformity of spinal curvature. In addition, otherrod systems provide mechanisms for longitudinal distraction andcompression of the hooks as required to account for the particularmedical indication. Similarly, the hook and rod systems provide a meansfor maintaining correct positioning of vertebrae during a vertebralfusion process as may be indicated to correct painful disc syndrome ordegenerative disc disease.

While the hook and rod spinal systems of the prior art have provided avery valuable and effective means for correcting spinal deformities orstabilizing spinal injuries, there remains a need for improvement ofcertain aspects of these spinal systems. For instance, many of the priorsystems have a limited ability to obtain correction of spinaldeformities by moving the fixation hooks perpendicularly with respect tothe rod, that is to pull the spine to a physiologically bent rod wherethe hooks are already engaged to a portion of a vertebra. Another areaopen for improvement concerns the ability to add hooks at any pointalong the spine at any time during a medical procedure to compensate forloss of correction of curvature or inaccurate preoperative planning ofhook placement. While A-P and lateral radiographs provide a great dealof information to allow the spinal surgeon to plan hook placement, it isoften necessary to modify this plan once the implantation procedure hasbegun due to unanticipated pathologies of the patient.

A further area of improvement for the hook and rod spinal systemsconcerns the ease of assembling the system. Consideration in recenttimes has been given to "top loading" the spinal rods. In this feature,the hooks are engaged to the appropriate vertebrae, the rod ispositioned relative to the hooks and the eyebolt or other fastener istightened, all posteriorly. Nevertheless, there still remains a need fora simpler and more efficient method for assembling this system toeliminate the "fiddle factor" that is present in most known hook and rodspinal systems.

SUMMARY OF THE INVENTION

The present invention contemplates a spinal implant system forcorrecting spinal deformities and abnormalities that uses an elongatedspinal rod configured to be implanted adjacent the spinal column andspanning across several vertebral levels. A number of fixation elements,such as spinal hooks, are provided for engaging vertebrae at a number ofvertebral levels. According to the present invention, at least some ofthe fixation elements includes an elongated stem projecting from thevertebra engaging portion. In one important aspect of the invention, rodconnector means are provided for connecting the stem of each fixationelement to the spinal rod. The rod connector means includes a connectorhaving a one-piece body defining a rod channel adapted to receive thespinal rod therethrough, a stem bore adapted to receive a stemtherethrough, and a threaded bore. A threaded set screw is providedwhich is adapted to be received within the threaded bore. The stem borehas a length through the body and the rod channel intersects the stembore along a portion of this length to permit contact between the rodand the stem of a fixation element when the rod is received within therod channel and the stem is received within the stem bore.

In one embodiment of the invention, the threaded bore intersects thestem bore to permit contact between the set screw and the stem withinthe stem bore as the set screw is threaded into the threaded bore. Asthe set screw is threaded further into the threaded bore, it presses thestem against the spinal rod to provide a clamped engagement and torestrain relative movement between the rod and the fixation element. Ina further embodiment, the threaded bore intersects the rod channel sothat the set screw bears against the spinal rod when the rod is withinthe rod channel. In this embodiment, as the set screw is threadedfurther into the threaded bore, it presses the rod against the stem ofthe fixation element to again provide a clamped engagement between therod and the stem of the fixation element.

In a further important aspect of the invention, the connector body ofthe rod connector means further defines a channel opening extending tothe rod channel which is sized to permit passage of the spinal rodtherethrough when the rod is to be received within the rod channel. Thischannel opening permits "top-loading" of the rod connector means whenthe spinal rod is already in position adjacent the spinal column. Thestem bore in the connector body has an elongated cross-section with alength along the long axis of the cross-section that is greater than thewidth of the fixation element stem. This greater length allows the stemto move back within the stem bore to allow the connector body to engagethe spinal rod even when the stem is extending through the stem bore.Once the connector body is disposed in its final implanted position, theset screw can be tightened to draw the stem and the spinal rod togetherinto a rigid construct.

In a further feature of the invention, the stem of the fixation elementscan include a groove defined along the length of the stem, the grooveforming opposite groove tips adapted to firmly grip the spinal rod. Thespinal rod can further include a spiral groove formed along its length,with the groove tips of the fixation element stem sized to fit withinthe spinal rod spiral groove. This feature of the invention adds agreater element of security against the fixation element stem slidingalong the length of the spinal rod.

The spinal implant system of the present invention further contemplatesa lateral offset coupler which permits adjustment of the lateralposition of a fixation element relative to the spinal rod. In oneembodiment, the lateral offset coupler includes an offset body withmeans for engaging a fixation element, and a stem extending from theoffset body. The stem is preferably configured identically to thefixation element stem described above so that the same rod connectormeans can be used to connect the lateral offset coupler to the spinalrod. In one specific embodiment of the lateral offset coupler, theoffset body is perpendicularly offset from the stem to permitsuperior/inferior offset of the fixation element when the lateral offsetcoupler is connected to the spinal rod.

One feature common to the stem of the fixation elements and the stem ofthe lateral offset coupler resides in external threads formed along aportion of the length of both stems. The threads are adapted to receivea correspondingly threaded nut which forms part of a means fortemporarily fastening the components to the rod connector means.Specifically, in the case of the threaded stem of the fixation elements,the stem is long enough to extend significantly above the level of thespinal rod when the rod is initially positioned near the spinal column.When the rod and stem are situated within the rod connector body, thenut can be threaded onto the threads of the fixation element stem. Asthe nut is tightened down onto the stem threads, it bears against theconnector body, pushing the body, and the spinal rod with it, closer tothe vertebra engaging portion of the fixation element. In other words,the present invention provides for a method of implanting a spinalsystem in which the bulk of the instrumentation procedure can beaccomplished at a level dorsal to the instrumented vertebrae, allowingeasier unencumbered assembly. When the orientation of the construct andarrangement of vertebral fixation elements meets with the surgeon'ssatisfaction, the construct can be drawn anteriorly down to its finalimplant level adjacent the vertebrae by threading each of the nuts downon the threaded stems of the fixation elements. Once the spinal rod hasreached its final location, the set screws in each of the rod connectormeans can be tightened to firmly clamp rod to fixation element, therebycompleting the implant construct. The same components can be used as areduction apparatus to draw a misplaced vertebra into alignment withadjacent properly positioned vertebrae.

It is therefore one object of the invention to provide a spinal implantsystem that dispenses with the "fiddle factor" associated with priorsystems in which the fixation components must be pre-loaded onto thespinal rod. A further object resides in features of the presentinventive system that provide top-loading of rod connectors that can beused in a variety of orientations to connect fixation elements,transverse connectors and lateral couplers alike.

A benefit attained by the present invention is the ability to initiallyinstrument the spine at a higher posterior level and then subsequentlydraw the construct down to its final position adjacent the vertebrae. Afurther object resides in providing a system that allows the surgeon toadd vertebral fixation elements or change the position or level ofinstrumentation while the spinal rod is oriented along the spinalcolumn.

Yet another object of the invention is to provide an implant systemhaving a reduced profile from prior rod systems. Other objects andbenefits of the present invention will become apparent uponconsideration of the following written description taken in conjunctionwith the accompanying figures.

DESCRIPTION OF THE FIGURES

FIG. 1 is a top elevational view of a spinal fixation system of theprior art, namely the TSRH® system of Danek Medical, Inc.

FIG. 2 is a partial top elevational view of a spinal fixation system inaccordance with the present invention showing various components of thesystem for engaging the vertebrae.

FIG. 3A is a side view of a rod connector and hook arrangementimplemented according to the present invention with a spinal hookclamped to longitudinal fixation rod.

FIG. 3B is a bottom partial cross-sectional view of the rod connectorand hook system shown in FIG. 3A taken along line 3D-3B as viewed in thedirection of the arrows.

FIG. 3C is a further side view of the rod connector and hook assembly asviewed rotated 90° from the appearance in FIG. 3A.

FIG. 4 is a side partial cross-sectional view of a rod connector andhook assembly in an alternative embodiment of the present invention.

FIG. 5 is a partial cutaway view of an offset coupler in accordance withthe present invention.

FIG. 6 is a top elevational view of the offset coupler component shownin FIG. 5.

FIG. 7 is an end view of the stem of the offset coupler shown in FIG. 6.

FIG. 8A is a top elevational view of a transverse coupler in accordancewith the present invention.

FIG. 8B is a side elevational view of the transverse coupler shown inFIG. 8A.

FIG. 9 is an end partial cross-sectional view of the transverseconnector assembly in accordance with the spinal fixation system of thepresent invention.

FIG. 10A is a side elevational view of a dual hook connector assembly inaccordance with the present invention.

FIG. 10B is a top elevational view of the dual hook connector shown inFIG. 10A.

FIG. 10C is a top elevational view of a dual hook connector shown inFIG. 10B modified to utilize a single set screw.

FIG. 11 is a pictorial representation of the spinal fixation system inaccordance with one embodiment illustrating one aspect of the method forimplanting the system into a patient.

FIG. 12 is a lateral pictorial representation of a portion of the spinalcolumn instrumented with the spinal fixation system in one aspect of thepresent invention.

FIG. 13A is a side view of a rod connector in accordance with anotherembodiment of the present invention.

FIG. 13B is a top view of the rod connector shown in FIG. 13A.

FIG. 14 is a side view of a facing hook assembly in accordance with oneaspect of the present invention.

FIG. 15 is a top cross-sectional view of the facing hook assembly shownin FIG. 14, taken along line 15--15 as viewed in the direction of thearrows.

FIG. 16 is a side view of a clamp half used in connection with thefacing hook assembly shown in FIG. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

Referring now to FIG. 2, a spinal fixation system 20 in accordance withthe present invention is illustrated. The system includes a pair ofbendable elongated spinal rods 21 situated on opposite sides of thespinal column and particularly the sagittal plane. The rods 21 asdepicted in FIG. 2 are shown extending from the sacrum to the upperlumbar vertebrae. It is understood, of course, that the rods can extendto the thoracic vertebrae or between any group of vertebrae in thespinal column as indicated to correct the particular spinal deformity ortreat the specific spinal problem.

In the construct of the spinal fixation system 20, a number of fixationhooks 25 are engaged to the rod 21 at various locations along thevertebral column. As in prior spinal fixation systems, such as the TSRH®system described above, these fixation hooks engage predeterminedsegments of the spinal column to provide the appropriate forces forfixation or correction of spinal deformities. Each of the fixation hooks25 is engaged to a respective rod 21 by way of a rod connector means 28.Other rod connectors means 29 are used to mount other components to thespinal rods 21, such as an offset coupler 32. The offset coupler 32provides a means for supporting a bone screw 33 offset from the fixationposition on the rod in the lateral and superior/inferior directions. Therod connector means 29 are also used to support a transverse coupler 35which also engages a fixation screw 33 at variable lateral distances. Atransverse connector 38 can be provided to add lateral stability andfixation between the two rods 21.

With this general description of the construct of the spinal fixationsystem 20 of the present invention, attention now can be turned to thespecific components of the system. One embodiment of the rod connectormeans 28 is shown in FIGS. 3A-3C. It can be seen that the rod connectormeans 28 provide a means for engaging a fixation element, such as hook25, to the spinal rod 21. The fixation hooks 25 includes an elongatedstem 26 and an integral claw portion 27 which engages a portion of avertebra. The rod connector means 28 includes a connector body 45 whichdefines a rod channel 47 through which the spinal rod 21 extends. In onespecific embodiment, the rod channel 47 includes a channel opening 48 sothat the rod connector means 28 can be "top-loaded" onto the spinal rod21. Alternatively, the channel opening 48 can be eliminated so that therod channel 47 is in effect a bore through the connector body 45. Inthis instance, with the "closed" rod channel configuration, the rodconnector means 28 must be preloaded onto the spinal rod prior toplacement of the rod in the patient. In this manner, the closed channelrod connector means would operate similar to the eyebolt fixationcomponent of the TSRH® system previously described. The open channelconfiguration is preferred to retain the flexibility afforded by thetop-loading capability. Top-loading means that a surgeon can add newfixation elements and rod connector means as necessary at virtually anystage of the spinal instrumentation procedure, even with the spinal rodin position adjacent the spine.

The connector body 45 of the rod connector means 28 further defines astem bore 49 which is oriented perpendicular to the rod channel 47 andwhich intersects the rod channel at an overlap portion 50. The stem boreis adapted to receive the fixation element stem 26 therethrough and, ascan be seen more particularly in FIG. 3B, can be in the shape of anelongated slot that is larger than the general width of stem 26.However, it is an essential feature of the rod connector means 28 of thepresent embodiment that the bore 49 include the bore/channel overlap 50to permit the stem 26 of the fixation hook 25 to contact the rod 21 whenthe rod is situated within the rod channel 47.

The body of the rod channel 47 defines a rod/channel overlap portion 51,as shown in FIG. 3B, which serves to retain the rod 21 within thechannel 47. The pressure between the stem 26 of the hook 25 and therod/channel overlap portion 51 of the connector body 45, clamps the rodto the rod connector means 28. This pressure is provided by way of a setscrew 58 which is threaded into a set screw bore 54. As can be seen inFIG. 3A, the set screw bore is oriented at an angle to both the stembore 49 and the rod channel 47 and intersects the stem bore 49 at anintersection 55. In this manner, a set screw 58 threaded into the bore54 can contact and apply pressure to the hook stem 26. As the set screw58 is threaded deeper into the set screw bore 54, the curved tip 58a ofthe screwy applies pressure to the stem and clamps the stem 26 and therod 21 between the connector body 45 and the set screw 58.

In this specific embodiment, the set screw 58 includes a driving head 59which can be of a typical hex configuration. When the driving head 59 isa hex head extending beyond the surface of the connector body 45, theangular orientation of the set screw bore 54 helps to reduce theposterior profile of the rod connector means 28. In addition, it hasbeen found that this particular angular orientation of the set screw 58often facilitates tightening the set screw within the bore 54. It is ofcourse understood that the driving head 59 can be replaced by a hexrecess for engagement to an allen head tool.

The rod 21 of one specific embodiment includes a feature for preventingthe rod connector means 28 from shifting along the length of the rod 21.In particular, the rod 21 includes a spiral groove 22 formed in theouter surface of the rod, as shown in FIGS. 3B and 3C. In addition, thestem 26 of the fixation hook 25 can include a pair of shallow grooves 40on opposite faces of the stem. The grooves form tips 41 at the edges ofthe grooves, which tips engage within the spiral groove 22 of the rod21. It has been found that the interface between the groove tips 41 andthe rod spiral groove 22 adds a greater degree of longitudinal stabilityto the rod connector means 28 to prevent the connector from slidingalong the rod during or after instrumentation. The groove 40 in the hookstem 26 provides a contoured surface for receiving the oval point 58a ofthe set screw 58. This allows for maximum frictional contact between theset screw 58 and the hook stem 26, thereby reducing the likelihood ofslippage in the posterior/anterior direction of the hook relative to theconnector 28. It has been found that the groove tips 41 can deformslightly when pressed against the spinal rod 21, with or without thespiral groove 22, to provide an additional frictional fit.

An alternative embodiment of the rod connector is shown in FIG. 4. Inthis embodiment, the rod connector means 60 includes a connector body 61which defines a rod channel 63. The body further defines a channelopening 64 which opens generally laterally relative to the body 61. Thebody 61 also defines a stem bore 68 through which the stem 26' of afixation hook 25' can extend. The channel opening 64 of the rod channel63 is oriented at a somewhat anterior angle to the stem bore 68. On theother hand, in the rod connector means 28 of the previous embodimentshown in FIG. 3A, the channel opening 48 extends generally parallel tothe stem bore 49.

The channel opening 64 of the connector body 61 is defined by a pair ofparallel faces 64a and 64b. These parallel faces 64a and 64b provide asurface along which the connector 60 slides along the rod 21' when theconnector is to be engaged to the rod. While the rod connector means 60is intended to be a top-loaded component, similar to the rod connectormeans 28, the engagement of the connector 60 to the spinal rod 21requires some degree of lateral manipulation to snap the rod through thechannel opening 64 into the rod channel 63. The lower parallel face 64bincludes a locking edge 65 at the channel opening 64 which helps retainthe rod 21' within the rod channel 63.

The stem bore 68 defines a bore/channel overlap 70, similar to thatfound in the rod connector means 28 of the previous embodiment. Thus,when the stem 26' of a fixation hook 25' extends through the stem bore68, the stem 26' can contact the rod 21'. This contact is maintained byway of a set screw 74 which is threaded into a set screw bore 72 at theupper arm of the channel 64 and particularly through the upper parallelface 64a. The set screw 74 includes a driving head 75 and a rod engagingtaper 76 at the opposite end of this set screw. This taper 76 isgenerally conical in shape and has a curvature which approximates thecurvature of the spinal rod 21'. In this specific embodiment, it can beseen that the rod 21' does not include the spiral groove 22 describedabove. Moreover, the stem 26' of the hook 25' does not include thegrooves 40 in the opposite faces of the stem. It has been found thatwith this configuration of rod connector means 60, the three points ofcontact to the rod 21' essentially eliminate the need for the spiralgroove 22 and stein groove 40. As can be seen from FIG. 4, the rod 21'is clamped between the rod channel 63, particularly at the locking edge65, the hook stem 26', and the tapered tip 76 of the set screw 74. Onthe other hand, as can be seen by comparison to FIG. 3A, the rod 21 isengaged only between the rod channel 47 and the grooved stem 26 of thehook 25. The manner in which the two rod connector means 28 and 60 snapon to the spinal rod 21 or 21' may dictate which of the particularconnectors is used at a specific level of instrumentation. It has beenfound that either of the two connectors 28 or 60 provide a solidengagement of the fixation hook 25 or 25' to the longitudinal spinalrod.

Both of the rod connector means 28 and 60 permit top-loading of theconnector to connect the fixation element stems to the spinal rod. Thechannel openings (48 and 64) allow the spinal rod to be slipped into therespective rod channels 47 and 63. The corresponding stem bores 49 and68 have an elongated cross-section in which the long axis of thecross-section is greater than the general width of the fixation elementstem 26. Thus, the stem is allowed to slide to one end of the bores49/68 providing clearance for the spinal rod to pass into the rodchannels. In the case of the rod connector means 28, this clearance isof greater importance to allow the rod to clear the rod/channel overlap51. On the other hand, the rod connector means 60 eliminates some ofthis manipulation since the stem bore 68 is at the opposite end of therod channel 63 from the channel opening 64.

Referring now to FIGS. 5-7, a further component of the spinal fixationsystem 20 of the present invention is shown. In particular the offsetcoupler 32 previously illustrated in FIG. 2, provides a means forengaging a bone fastener 33 (either a screw or bolt) to the spinal rod21. The offset coupler 32 includes a stem 79 (FIG. 6) which includesupper and lower grooves 80. The grooves define groove tips 81, as shownin FIG. 7. The offset coupler 32 further includes an offset body 83which is oriented generally perpendicular to the stem 79. In addition,as shown in FIG. 5, the offset body 83 angles downward somewhat from thelongitudinal axis of the stem 79 so that the screw bore 84 in the body83 is at or below the level of the spinal rod 21. The bore 84 throughthe body 83 also includes upper and lower countersunk portions 85.

As shown in FIGS. 2 and 5, the stem 79 of the offset coupler 32 can beengaged to the spinal rod 21 by way of a rod connector 29. In onespecific embodiment, the rod connector 29 can be the rod connector 28 orthe rod connector 60. However, as should be apparent from FIG. 5, therod/channel overlap 51 of the rod channel 47 is oriented at theunderside, or anterior side, of the spinal rod 21, as opposed to thelateral engagement shown in FIG. 3A. This orientation of the rodconnector 28/29 allows the stem 79 of the offset coupler 32 to contactthe spinal rod 21 at the posterior, or top, side of the rod.

The offset coupler 32 provides a means for engaging a bone fastener 33,such as a screw or bolt to the rod 21. The details of the threadedfastener 33 is shown in FIG. 5. In particular, the fastener 33 includesbone engaging threads 88 which are adapted to be threaded into thepedicle of a vertebra, such as a lumbar vertebra. At the opposite end ofthe fastener 33 are machine threads 89 which are adapted to engage athreaded nut 93. Between the machine threads 89 and the bone threads 88is an intermediate portion 90. This intermediate portion 90 includes anupper arcuate surface 91 which is seated against the undersidecountersink 85 of the screw bore 84 in the offset body 83. Similarly,the nut 93 includes an arcuate seat 94 which engages the uppercountersink 85 in the offset body 83.

It has been found with this specific embodiment of the threaded fastener33 that the engagement between the countersinks 85 and the arcuatesurfaces of the intermediate portion 90 and the nut 93 allows for somedegree of angulation of the fastener 33 relative to the offset coupler32. In practice it can be difficult to perfectly align the offsetcoupler 32 with the particular vertebral segment to be instrumented.Thus, the ability to orient the threaded fastener 33 relative to the rod21 enhances the ability of the surgeon to instrument the spine. Ofcourse, it is understood that in certain applications the threadedfastener 33 need not include the arcuate surface 91 and can simplyinclude a flat engagement surface, such as found in bone bolts having anintegral hex driving nut feature. When the threaded fastener 33 is abone bolt, it is anticipated that the bolt would be first threaded intothe particular vertebra at the level of instrumentation. The offsetcoupler 32 is then be engaged to the bolt and subsequently fastened tothe spinal rod 21 by way of a rod connector 29. Alternatively, theoffset coupler 32 may already be engaged to the rod 21 by a connector29, after which the coupler 32 and threaded fastener 33 are pulledtogether and engaged. The threaded fastener 33 may be a bone screw whichdoes not include an intermediate portion 90 that engages the undersideof the offset body 83. In this instance, it can be expected that theoffset body 83 is configured to project a little further below thespinal rod 21 to contact the surface of the vertebra when the screwy isthreaded into the bone.

A transverse coupler 35 in accordance with the present invention isshown in FIGS. 8A and 8B. The transverse coupler 35 provides for lateraloffset engagement of a threaded fastener 33 between the bone and spinalrod 21. The transverse coupler 35 is similar to the offset coupler 32except that it does not include an anterior/posterior offset feature.Specifically, the transverse coupler 35 includes a stem 96, which can bea grooved stem such as the stem 79 of the offset coupler 32. Integralwith the stem 96 is an offset body 97, which includes an anterior offsetportion 98 to bring the body 97 closer to the vertebra when thetransverse coupler 35 is engaged to the spinal rod 21. The offset body97 includes a screw slot 99 having upper and lower countersinks 100. Theslot 99 can simply be a circular bore or can be somewhat elongated toallow for further variation in lateral position of the threaded fastener33 relative to the transverse coupler 35. In the case of both the offsetcoupler 32 and the transverse coupler 35, it is anticipated that therespective stems 79 and 96 are long enough to allow for some lateral ortransverse variation in position. In addition, the stems 79 and 96 caninclude threads along their length, such as threads 101 shown in FIG.8B. These threads 101 are adapted to receive a nut which is threadedonto the stem when the stem is loosely disposed within a rod connector29 in position on the spinal rod 21. The threads 101 and the additionaltemporary nut can be used to draw the transverse coupler 35, andparticularly the threaded fastener 33 supported by the coupler, towardthe spinal rod 21. That is, as the nut is threaded onto the threads 101,the rod 21 and the threaded fastener 33 are pulled together. Once theappropriate orientation of rod to fastener is achieved, the rodconnector 29 and particularly the set screw of the rod connector, can betightened to clamp the stem 96 to the rod 21. Once the rod connector 29has clamped the transverse coupler 35 to the rod 21, the temporary nutcan be removed and the excess portion of the stem extending beyond therod connector can be sheared off and removed.

The spinal fixation system 20 of the present invention furthercontemplates the use of a transverse connector 38 to provide transverseor lateral interconnection between the two spinal rods 21. As shown inFIG. 9, the transverse connector 38 includes a stem 105 terminating atone end in a head portion 106. The stem of the transverse connector isconfigured to pass through stem bores of rod connectors 29 engaged toeach of the two rods 21. As discussed above, the rod connectors 29 canbe configured as either the rod connector 28 or 60. Alternatively, therod connectors 29 can be configured as shown in FIG. 9 to include a rodchannel 108 and a posteriorly oriented set screw bore 110. The stem bore109 projects perpendicularly to the set screw bore 110, but parallel tothe opening of the rod channel 108. The set screw 111 can include a hexhead recess to receive an allen head tool. In this manner, the rodconnector 29 is readily adapted for receiving a driving tool directlyposterior to the rod and transverse connector 38. The set screw 111,which is preferably similar to the set screw 58, which includes an ovalpoint for engaging the stem 105 of the transverse connector 38. Again,as with the transverse coupler 35, the stem 105 of the transverseconnector 38 can be threaded to allow a temporary nut to be tightenedonto the stem. As the temporary nut is tightened onto the stem, thespinal rods 21 engaged by the rod connectors 29 are drawn together. Thehead 106 at the one end of the transverse connector 38 provides anadditional reaction surface in combination with the temporary nut. Oncethe appropriate position between the two rods 21 has been achieved, therod connectors 29 can be tightened to firmly engage the stem 105 of thetransverse connector 38 to each of the rods, and the temporary nutremoved.

Referring now to FIGS. 10A and 10B, a dual hook connector 115 is shownwhich provides means for engaging a pair of hooks to a spinal rod by wayof a single connector. The dual hook connector 115 includes a connectorbody 118 which receives the stems 24 of a pair of hooks. Specifically,the hooks can be a hook such as hook 25 having a stem 26, as well as adifferently configured laminar hook 116 having a stem 117. The two hookscan have their claws facing each other to engage the lamina of avertebra therebetween. Each of the stems 26 and 117 extend through arespective stem bore 120 defined in the body 118. A pair of set screwbores 121 intersect the stem bores 120 so that a pair of set screws (notshown) can be threaded therein to clamp the stems to the spinal rod. Thedistance between the stem bores 120 and set screw bores 121 areestablished to permit sufficient space between the claws of therespective hooks 25 and 116 to engage the lamina at a particularvertebral level. It is understood that the dual hook connector 115 canbe configured in the style of the open connectors 28 or 60 describedabove. In other words, the invention contemplates a dual hook connectorin which two open connectors, such as connector 28, are integrallydisposed side-by-side to support two spinal hooks.

In a modification to the dual hook connector, a connector 115" shown inFIG. 10C is configured to utilize a single set screw 122 to clamp thestems 26" of laminar hooks to a spinal rod 21. The connector 115"includes a body 118" having a pair of parallel oblong stem bores 120"formed therein. Intersecting each of the stem bores 120" is a set screwbore 121". The set screw 122, when threaded into the bore 121" contactsboth hook stems 26" to clamp them against the rod 21. The stems 26" canbe circular in cross section, as shown in FIG. 10C, or can have a crosssection as shown in FIG. 10B.

A further transverse coupler 130 is illustrated in FIG. 11. Thistransverse coupler 130 includes a stem 131 and offset body 132 at oneend of the stem. The offset body 132 is configured to support a threadedfastener 33 which is engaged to the body 132 by way of nut 93. As isapparent from this figure, the offset body 132 is at the same level asthe stem 131 and does not include any posterior/anterior orsuperior/inferior offset. This transverse coupler 130, and particularlyits stem 131, can be configured similar to the stem 96 of the coupler 35to include a channel and outer threads.

Certain features of the method of instrumenting the spine using thesystem 20 of the present invention can be understood with reference toFIG. 11. In this figure, a spinal rod 21" is shown instrumented with apair of hooks 25" and a threaded fastener 33. The stems 26" of the hooks25" are engaged to the rod 21" by way of a rod connector 29. In thisspecific embodiment, the rod connector is the connector 29 having a hexrecess set screw 111. Alternatively, the rod connector can be either ofthe rod connectors 28 or 60 previously described.

As can be seen in FIG. 11, the stems 26 of the hooks 25 are long enoughto project significantly outward from the rod 21. These stems are shownin their configuration immediately after having been installed in thespine. The stems, which are preferably about two inches long, allow moreready top-loading of the rod when the hooks are already engaged at theparticular vertebral level. In prior systems, the vertebral hooks have arelatively short stem for engagement by the rod instrumentation. Thisadds to the "fiddle factor" in completing the instrumentation. On theother hand, the present invention contemplates a much longer stem to thehooks, which stem can be severed at a break line 125 once the hooks havebeen fastened to the spinal rod 21. In accordance with the presentinvention, the hooks are engaged at the vertebra with the stemsextending posteriorly. The rod and rod connector 29 can then betop-loaded onto the stem with the hook stem extending through the boresin the connectors 29. A temporary nut 124 can be threaded onto thethreads 123 of each of the hook stems 26 to draw the rod 21 and theinstrumented vertebra together. Once the appropriate relationshipbetween rod and vertebra has been achieved, the set screw 111 of the rodconnector 29 can be tightened to clamp the stem 26 to the rod 21. Atthis point, the temporary nut 124 is removed and the stem shortened bysevering at the break point 125.

The spinal fixation system of the present invention can also be used asa reduction apparatus. As shown in FIG. 12, a displaced vertebra V₁ isinstrumented between two normally positioned vertebrae V₂ and V₃. Thespinal rod 21 is bent to approximate the spinal physiology of thesubject vertebra. The normal vertebra V₁ and V₃ are engaged by the clawsof spinal hooks 25. The hooks 25 are attached to the spinal rod 21 byway of rod connectors, such as rod connectors 29 described above. Thedisplaced vertebra V₁ is instrumented with laminar hooks 135 and 137.Each of the hooks 135 and 137 has a corresponding elongated stem 136 and138, respectively. The stems extend through a dual hook connector, suchas connector 115 described with respect to FIGS. 10A and 10B. A pair ofnuts 139 and 140 are threaded onto stems 136 and 138, respectively. Asthe nuts are tightened down onto their corresponding stems, the hooks135 and 137 draw the displaced vertebra V₁ toward the spinal rod 21, inthe direction of the arrows 142. The nuts 139 and 140 are continuallytightened onto the stems 136 and 138 until the vertebra V₁ is in properalignment relative to the other instrumented vertebrae V₂ and V₃.

Thus can be seen that the spinal fixation system according to thepresent invention includes multi-level instrumentation capabilitieswhich can be used for two purposes. The first purpose is to permitinstrumentation at a higher level above the vertebrae and then be drawndown to a level immediately adjacent the vertebrae. The second use is asa reduction apparatus to draw a displaced vertebra into properphysiological alignment.

Alternative embodiments of certain components of the spinal fixationsystem of the present invention are also contemplated. For instance,referring now to FIGS. 13A and 13B, a closed rod connector 145 is shown.The rod connector 145 includes a body 146 which defines a rod channel147 therethrough. The rod channel 147 is generally oblong in shape andis defined by a pair of overlapping bores 148 and 149. The bore 148 hasapproximately the same diameter as the spinal rod 155, while the bore149 portion of the rod channel 147 has a somewhat larger diameter. Therod connector 145 is a closed connector in the sense that the rodchannel 147 does not include a channel opening through the sidewall ofthe body 146. Thus, the connector 145 must be pre-loaded onto the spinalrod 155 prior to instrumentation of the vertebra. Initially duringinstrumentation, the rod 155 will nominally reside within the diameter148 of the channel 147.

The rod connector 145 further includes a stem channel 150 which includesa channel opening 151 through the sidewall of body 146. The channelopening 151 allows the rod connector 145 to readily engage the stem 156of a spinal hook already engaged to a vertebra. The elongated rodchannel 147 allows the spinal rod 155 to be situated away from the stemchannel 150 until the stem 156 is moved through the channel opening 151.

The rod channel 147 and the stem channel 150 overlap at a portion 152.This overlap 152 allows the spinal rod 155 to be pushed into directcontact with the stem 156. The stem channel 150 also includes an overlap153 which holds the stem 156 in place. It can be seen that the stem 156includes opposite fiat surfaces 157 to provide a greater contact surfacebetween the stem 156, and the stem channel 150 and spinal rod 155.

The body 146 of the rod connector 145 further defines a set screw bore154 which intersects the rod channel 147. A set screw 160 is thenthreaded into the bore 154 so that the tip 161 contacts the spinal rod155 and urges it into frictional engagement with the stem 156.

In a further aspect of the invention, a dual facing hook assembly 170,shown in FIGS. 14-16, is provided which includes a pair of hooks 171 and172 which can be instrumented on a vertebra in a facing orientation. Thehooks 171 and 172 include respective stems 174 and 175. In a novelfeature of this assembly 170, each of the stems 174 and 175 includespartial threads 176 and 177 respectively. These threads are formed sothat when the two stems 174 and 175 are adjacent one another, as shownin FIG. 15, a fully threaded cylindrical rod is formed. A nut 180 canthen be threaded onto the combined stems 174 and 175 to clamp the stemstogether and to provide a means for engaging a spinal rod 21.

The assembly 170 further includes a pair of clamp halves 185 which aredesigned to trap a spinal rod 21 therebetween in clamped engagement.Each clamp half 185 defines half of a bore 186 so that when the twohalves are combined they form a bore for receiving the rod 21therethrough. In addition, each clamp half defines a second half bore187 which is configured to receive the two stems 174 and 175 when thetwo clamp halves are combined. In one feature of this embodiment, theclamp halves 185 and the stems 174 and 175 are configured for keyedengagement. Specifically, the stems include flat opposite surfaces 178which correspond to similarly configured flat surfaces 188 of the secondhalf bore 187 in each clamp half 185. This keyed arrangement providesfor a specific orientation of the clamp halves 187 relative to the stems174 and 175 so that the spinal rod 21 is oriented parallel to theopening of the spinal hooks 171 and 172.

It can be seen that the present invention provides a much easier methodfor assembly in which the construct is formulated at a higher level andthen ultimately brought anteriorly down to a lower profile levelimmediately adjacent the spine. This facilitates the addition of otherhooks and connectors if and when it is determined that the proposedinstrumentation plan requires modification. With the spinal rodsinitially oriented at a higher dorsal or posterior level above thevertebrae, the addition of components is more easily achieved.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected.

What is claimed:
 1. A spinal implant system for correcting spinaldeformities and abnormalities, comprising:an elongated spinal rodconfigured to be implanted adjacent the spinal column of a patientspanning across several vertebral levels; a number of fixation elementsfor engaging vertebra at a number of vertebral levels, each of saidnumber of fixation elements having a vertebra engaging portion and anelongated stem extending from said vertebra engaging portion, said stemof each of said number of fixation elements including opposite flatsurfaces extending along the length of said stem, thereby increasing thearea of contact between said stem and said rod, and between said stemand said connector body when said stem is clamped within said stemchannel; a number of rod connector means for connecting each of saidfixation elements to said spinal rod, each of said rod connector meansincludinga connector having a body defining a rod bore adapted toreceive said spinal rod therethrough, a stem channel adapted to receivesaid stem therethrough, and a threaded bore; a threaded set screwadapted to be received within said threaded bore, wherein said stemchannel has a length through said body and said rod bore intersects saidstem channel along a portion of said length to permit contact betweensaid rod and said stem when the rod is received within said rod bore andthe stem is received within said stem channel, wherein said body definesa channel opening extending to said stem channel and sized to permitpassage of said stem through said channel opening to said stem channelwhen said rod is received within said rod bore, and further wherein,said threaded bore intersects said bore to permit contact between saidset screw and said rod when the set screw is threaded into the threadedbore, whereby said stem and said rod are in clamped engagement when saidset screw is threaded into said threaded bore to restrain relativemovement between said rod and said fixation element.
 2. The spinalimplant system of claim 1, wherein said rod bore is defined by a pair ofintersecting bores, a first one of said intersecting bores intersectingsaid stem channel and a second one of said intersecting boresintersecting said threaded bore.
 3. The spinal implant system of claim1, wherein said spinal rod is generally circular in cross-section andsaid set screw includes a tapered tip for engaging said rod.
 4. Thespinal implant system of claim 1, wherein said body of said connectorincludes an overlap portion to hold said stem in place.
 5. The spinalimplant system of claim 4, wherein:said rod bore in defined by a pair ofintersecting bores, a first one of said intersecting bores intersectingsaid stem channel and a second one of said intersecting boresintersecting said threaded bore; and wherein said spinal rod isgenerally circular in cross-section and said set screw includes atapered tip for engaging said rod.
 6. A spinal implant system forcorrecting spinal deformaties and abnormalities, comprising:an elongatedspinal rod configured to be implanted adjacent the spinal column of apatient spanning across several vertebral levels; a number of fixationelements for engaging vertebra at a number of vertebral levels, each ofsaid number of fixation elements having a vertebra engaging portion andan elongated stem extending from said vertebra engaging portion; anumber of rod connector means for connecting each of said fixationelements to said spinal rod, each of said rod connector means includingaconnector having a body defining a rod bore adapted to receive saidspinal rod therethrough, a stem channel adapted to receive said stemtherethrough, and a threaded bore; a threaded set screw adapted to bereceived within said threaded bore, wherein said rod bore in defined bya pair of intersecting bores, a first one of said intersecting boresintersecting said stem channel and a second one of said intersectingbores intersecting said threaded bore, said stem channel has a lengththrough said body and said rod bore intersects said stem channel along aportion of said length to permit contact between said rod and said stemwhen the rod is received within said rod bore and the stem is receivedwithin said stem channel, wherein said body defines a channel openingextending to said stem channel and sized to permit passage of said stemthrough said channel opening to said stem channel when said rod isreceived within said second rod bore, and further wherein, said threadedbore intersects said bore to permit contact between said set screw andsaid rod when the set screw is threaded into the threaded bore, wherebysaid stem and said rod are in clamped engagement when said set screw isthreaded into said threaded bore to restrain relative movement betweensaid rod and said fixation element.
 7. The spinal implant system ofclaim 6, wherein said stem of each of said number of fixation elementsincludes opposite flat surfaces extending along the length of said stem,thereby increasing the area of contact between said stem and said rod,and between said stem and said connector body when said stem is clampedwithin said stem channel.
 8. The spinal implant system of claim 6,wherein said spinal rod is generally circular in cross-section and saidset screw includes a tapered tip for engaging said rod.
 9. The spinalimplant system of claim 6, wherein said body of said connector includesan overlap portion to hold said stem in place.
 10. The spinal implantsystem of claim 6, wherein said first one of said pair of intersectingbores has a first diameter, and said second one of said pair ofintersecting bores has a second diameter, and said first diameter islarger than said second diameter.
 11. The spinal system of claim 10,wherein:said stem of each of said number of fixation elements includesopposite flat surfaces extending along the length of said stem, therebyincreasing the area of contact between said stem and said rod, andbetween said stem and said connector body when said stem is clampedwithin said stem channel; and wherein said spinal rod is generallycircular in cross-section and said set screw includes a tapered tip forengaging said rod.
 12. A spinal implant system for correcting spinaldeformities and abnormalities, comprising:an elongated spinal rodconfigured to be implanted adjacent the spinal column of a patientspanning across several vertebral levels; a dual facing hook assemblyfor engaging a vertebra at opposite sides of a transverse process of thevertebra, said assembly includinga pair of spinal hooks each having avertebra engaging portion and an elongated stem extending from saidvertebra engaging portion, said elongated stems of said pair of hookshaving complementary transverse cross-sections so that said elongatedstems can be juxtaposed to form a substantially constant diameterelongated composite stem, said stems further being externally threadedso that said composite stem defines a continuously threaded outersurface; a pair of clamp halves, each having a stem bore therethroughfor receiving said composite stem therethrough and defining a half bore,the pair of clamp halves adapted to clamp said spinal rod between saidhalf bore portions of said clamp halves; and a threaded nut adapted tobe threaded onto said threaded outer surface of said composite stem,whereby said nut clamps said clamp halves and said spinal rod to saidcomposite stem, thereby connecting said dual facing hooks to said spinalrod.
 13. The spinal implant system of claim 12, wherein:said compositestem and said stem bores through each of said pair of clamp halves aremutually keyed.
 14. The spinal implant system of claim 12, wherein saidspinal rod is generally circular in cross-section.
 15. The spinalimplant system of claim 12, further comprising:a number of fixationelements for engaging vertebra at a number of vertebral levels, each ofsaid number of fixation elements having a vertebra engaging portion andan elongated stem extending from said vertebra engaging portion; anumber of rod connectors for connecting each of said number of fixationelements to said spinal rod, each of said number of rod connectorsincludinga connector body defining a rod bore adapted to receive saidspinal rod therethrough, a stem channel adapted to received said stemtherethrough, and a threaded bore; a threaded set screw adapted to bereceived within said threaded bore, and wherein the threaded boreintersects said bore to permit contact between said set screw and saidrod when the set screw is threaded into the threaded bore, whereby saidstem and said rod are in clamped engagement when said set screw isthreaded into said threaded bore to restrain relative movement betweensaid rod and said fixation element.